Hi Carol
I use seal mt tissue for different reasons.
Seal Colour Mount- this is a very durable and easy to use material, it is non removable and good for rc and colour work.( since the mount will last longer than a colour photograph I do not worry about so called archival rating with this tissue.

Seal Archival - this is a removable tissue and a bit harder to work with and you can use it at a lower temp.( I have had a problem using this tissue with inkjet prints* changed the colour of the print 8hrs afterwards* ) it is also not as agressive as colour mount.(with fibre prints I use a large border under the mat so that the corners coming up do not become a problem) I have never tried to make this mount reversable as Seal Claims.

these two mount materials are to be used with heat. There are also many cold mount methods to use but you do need a small laminator machine to do this.